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Status of ULE-HPGe Experiment for WIMP Search
Li Xin (Tsinghua University)KIMS collaboration
Feb. 7th, 2006
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Motivation
5g Ge
1cpd
Low mass Dark Matter candidate search - Low energy threshold necessary - Use 5g of prototype Ge detector ( plan to upgrade up to 1 kg )
Expected threshold: ~100eV
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Current System Setup
HPGe: -500VCsI(Tl): -1300V
H.V. (CEAN 1527) Amp. (CANBERRA 2026)
Shaping time: 6usGain: ×20
ULE - HPGe detector FADC & VME crate
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DAQ System
► DAQ device:DAQ device:
4-channel FADC4-channel FADC
SR=64MHz, 12bitSR=64MHz, 12bit
64 us window64 us window
USB2.0 interfaceUSB2.0 interface
Typical signals:
HPGe High gain(0~9keV)
HPGe Low gain(0~100keV)
CsI(Tl) channel(current signal)
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X-ray Generator
(From http://www.amptek.com )
LiTaO3
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(From http://www.amptek.com )
X-ray Generator
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Structure of the HPGe Detector
The carbon window can stop the particle with the energy less than about 1.5keV.
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HPGe Calibration – high gain channel
Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray
After gain correction and pedestal shift correction
2
113.13
12.9617
offset eV
ndf
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HPGe Calibration – low gain channel
Peaks:
Np (L X-ray), Ag (K X-ray), Am (alpha decay gamma)
2
0.0694
20.67
offset keV
ndf
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CsI Calibration
2
2.487
10.4607
offset keV
ndf
Gamma energy:
Cd-109 (Ag X-ray): 22.577 keV
Am-241: 59.5412 keV
U-238 (Th-234): 92.6 keV
Co-57: 123.66 keV
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PSD Parameters for CsI noise reduction
T-bar of CsI (Tl) Detail
Red: background files (Oct. 4th ~ Oct. 18th)Blue: calibration file (Co-57)Green: neutron file Threshold for CsI: ~10keV
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Neutron Recoil Data for HPGe
Energy spectrum
Source: Cf-252 (outside Pb shielding)Time: Nov. 2nd, 14:00~19:00
Time coincidence relation (1D)
Detail
Time coincidence relation (2D)
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Threshold for HPGeThreshold Pulse shape (270 ~ 290 eV)
Hardware threshold: ~ 150 eVElectronic noise level: τ~ 13 eV
Threshold for HPGe: 300eV
Energy spectrum of background pedestal shape fitting
50ln(1/ ) 13 ln(10 ) 150( )E h eV
exp( )E
h
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Background Data Analysis
datedate ThresholThreshold (keV)d (keV)
Total Total countscounts
Vetoed Vetoed countscounts
Background Background level (cpd)level (cpd)
Veto Veto efficiencyefficiency
Oct. 4th ~ Oct. 4th ~ 18th18th
0.30.3 802802 487487 44.182644.1826 60.7232%60.7232%
Oct. 4th ~ Oct. 4th ~ 18th18th
11 772772 479479 41.096941.0969 62.0466%62.0466%
High gain channel Low gain channel
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Background Data Analysis
datedate Threshold Threshold (keV)(keV)
Total Total countscounts
Vetoed Vetoed countscounts
Background Background level (cpd)level (cpd)
Veto Veto efficiencyefficiency
Oct. 18th ~ Oct. 18th ~ 31th31th
0.30.3 611611 368368 44.182644.1826 60.7232%60.7232%
Oct. 18th ~ Oct. 18th ~ 31th31th
11 587587 361361 45.033445.0334 61.4991%61.4991%
High gain channel Low gain channel
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Background after Neutron Run
datedate Threshold Threshold (keV)(keV)
Total Total countscounts
Vetoed Vetoed countscounts
Background Background level (cpd)level (cpd)
Veto Veto efficiencyefficiency
Nov. 3rd ~ Nov. 3rd ~ 11th11th
0.30.3 504504 294294 47.151847.1518 58.3333%58.3333%
Nov. 3th ~ Nov. 3th ~ 11th11th
11 465465 286286 40.191340.1913 61.5054%61.5054%
High gain channel Low gain channel
10keV peak
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Background with Strong γSource Outside
datedate Threshold Threshold (keV)(keV)
Total Total countscounts
Vetoed Vetoed countscounts
Background Background level (cpd)level (cpd)
Veto Veto efficiencyefficiency
Nov. 11th ~ Nov. 11th ~ 25th25th
0.30.3 830830 516516 44.440244.4402 62.1687%62.1687%
Nov. 11th ~ Nov. 11th ~ 25th25th
11 791791 508508 39.744139.7441 64.2225%64.2225%
High gain channel Low gain channel
Source: U-238, Th-232, Eu-152 (Outside Pb shielding)
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Summary
1. The ULE-HPGe system has been set up and
the data taking has been run for several
months.
2. Background level: abut 40
count/kg/day/keV (not from external
gamma)
3. Veto efficiency: about 60%
4. Software threshold: about 300 eV5. Question:
(1). Is the background level acceptable?
(2). Is the energy threshold correct?
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In the future…
1. Parameter selection for electronic system
2. Pulse shape study in low-energy region, and more
accurate calibration
3. Monte-Carlo simulation for external and internal
neutron, and build neutron shielding if necessary
4. Internal background study for HPGe and CsI(Tl)